Hazardous Earth SG3 Flashcards
Define Earthquake
Result from the sudden failure of rock within the lithosphere, as a result of a build up of pressure within the rocks
What are the three stages of making an earthquake?
1) Gradual build up of tectonic strain which stores elastic energy in crustal rocks
2) When the pressure exceeds the strength of the fault (a threshold event) the rock fractures
3) This produces the sudden release of energy creating seismic waves
What are the 4 locations earthquakes are concentrated in?
Mid ocean ridge at Divergent boundaries, Ocean trench and Island arcs at Convergent boundaries, Collisional zones, Conservative plate margins
Define Focus
The point of failure of the rocks, where the stress is suddenly released
Define Epicentre
Immediately above the point of failure (focus) on the earth’s surface, where most damage is likely to occur
How deep are shallow focus earthquakes?
0-70km
What % of earthquakes have shallow focus depths?
75%
How deep are intermediate focus earthquakes?
70-300km
How deep are deep focus earthquakes?
300-700km
What detects and records seismic waves?
Seismometer
What are the three types of wave?
Primary (P), Secondary (S) and Surface waves (L)
What can primary (P) waves pass through?
Solids and liquids
What can secondary (S) waves pass through?
Solids only
How much slower is the S wave than the P wave?
1/2 the speed of the P wave
Define Magnitude
Refers to the level of energy released by the earthquake
What three scales can be used to assess magnitude?
Richter Scale, Moment Magnitude Scale, Modified Mercalli Scale
How does the Richter Scale assess an earthquake’s energy?
Uses the amplitude of seismic waves to determine earthquake magnitude
How does the Moment Magnitude Scale assess an earthquake’s energy?
Measures magnitude based on physical movement e.g. size of a fault rupture, amount of slip displacement
How does the Modified Mercalli Scale assess an earthquake’s energy?
Relates ground movement with impacts that can be seen/felt by anyone in the affected location
What are five factors influencing intensity?
Distance from epicentre, Depth of focus, Magnitude, Geology, Building standards
Define Fault Scarp
A small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other
Define Normal Fault
The result of tension, with rocks displaced downwards relative to the other (FUN)
Define Reverse Fault
The result of compression, rocks are displaced upwards relative to the other (HUR)
Define Strike Slip Fault
The result of shear stress, rocks are displaced horizontally
What boundary are normal faults found at?
Divergent
What boundary are reverse fault found at?
Convergent
What boundary are strike slip faults found at?
Conservative
What is an example of a rift valley?
Great African Rift Valley
How was the Great African Rift Valley formed?
The thinning of the continental crust as a result of extensional forces from plate movement has resulted in faults and sunken valleys known as a graben
Define Escarpment
A steep slope or long cliff that forms as an effect of faulting or erosion and separates two relatively levelled areas having different elevations
What is the primary hazard of an earthquake?
Ground shaking - associated with the high amplitude L waves travelling through the surface layers of the earth
What are 4 primary hazards associated with an earthquake?
Damage to buildings, Liquefaction, Landslide/Avalanche, Tsunami
What are 5 factors which can affect people’s perceptions of earthquakes?
Religion, Past experiences, Education, Personality, Wealth
How many earthquakes does California have each year?
Around 10,000
How can you mitigate the event of an earthquake?
Nothing can be done to prevent an earthquake
How can you mitigate the vulnerability of an earthquake?
Monitoring, Community preparedness, Evacuation and Warning, Community adaption, Land use mapping of hazards, Aseismic design, Shut down of utilities
How can you mitigate the loss of an earthquake?
Emergency aid, Search and rescue, Insurance, Resources to help rebuild
